A technology to produce a molded article having a desired shape is known in which a molding material composed of a bundle-like aggregate of discontinuous reinforcing fibers (for example, carbon fibers) (hereinafter, also referred to as fiber bundle) and a matrix resin is used and it is molded by heating and pressurizing. In such a molding material, a molding material comprising a fiber bundle having a large number of single fibers is excellent in flowability at the time of molding, but tends to be inferior in mechanical properties of a molded article. On the other hand, a fiber bundle adjusted to an arbitrary number of single fibers is used as a fiber bundle in the molding material, aiming to satisfy both the flowability at the time of molding and the mechanical properties of the molded article.
As a method of adjusting the number of single fibers of a fiber bundle, for example, JP 2002-255448 A and JP 2004-100132 A disclose methods of performing fiber splitting using a plurality of fiber bundle winding bodies prepared by winding a plurality of fiber bundles in advance. In those methods, however, because the number of single fibers of each fiber bundle treated in advance is restricted, the adjustment range is limited and, therefore, it is difficult to adjust to a desired number of single fibers.
Further, for example, JP 2013-49208 A, JP 2014-30913 A and Japanese Patent No. 5512908 disclose methods of longitudinally slitting a fiber bundle to a desired number of single fibers by using disk-shaped rotary blades. In those methods, although it is possible to adjust the number of single fibers by changing the pitch of the rotary blades, since the fiber bundle longitudinally slit over the entire length in the longitudinal direction has no convergence property, the yarn after the longitudinal slit tends to become difficult in handling such as winding it on a bobbin or unwinding the fiber bundle from the bobbin. In addition, when conveying the fiber bundle after the longitudinal slitting, the split end-like fiber bundle generated by the longitudinal slit may be wrapped around a guide roll, a feed roll or the like, which may not be easy to convey.
Further, WO 2012/105080 discloses a method of cutting a fiber bundle to a predetermined length at the same time as a longitudinal slit by a split-fiber cutter having a lateral blade perpendicular to the fiber direction in addition to a longitudinal blade having a longitudinal slit function in a direction parallel to the fiber direction. According to that method, it becomes unnecessary to once wind the fiber bundle after the longitudinal slit to the bobbin and transport it, and the handling property is improved. However, since the split-fiber cutter has the longitudinal blade and the lateral blade, when one of the blades reaches the cutting life first, an obstacle arises that the entire blade has to be exchanged.
As described above, to produce a molded article having fluidity and mechanical properties, a fiber bundle adjusted to an arbitrary number of single fibers is necessary.
Furthermore, in passing through the above-described longitudinal slit process at a state where a fiber bundle is twisted such as twist exists in the fiber bundle itself or twist occurs during traveling of the fiber bundle at the fiber splitting process, because crossing fiber bundles are cut in the longitudinal direction, a problem occurs in that the fiber bundle is cut at a small length before and after the longitudinal slitting process and the longitudinal slitting cannot be continuously performed.
Accordingly, it could be helpful to provide a method and a device for manufacturing a partial split-fiber fiber bundle capable of continuously and stably slitting a fiber bundle. In particular, it could be helpful to provide a method and a device for manufacturing a partial split-fiber fiber bundle enabling a continuous slitting without being concerned about the exchange life of a rotary blade even in a fiber bundle including twist or a fiber bundle of a large tow having a large number of single fibers, and a partial split-fiber fiber bundle obtained by such manufacturing method and manufacturing device.